1. A Field of the Invention
This invention relates to a method of preparing a molded body (mold and mold material) at a low cost, which body has air permeability throughout it, good thermal conductivity and heat resistance, and easy workability.
2. Prior Art
Conventionally, forming molds having air permeability, and good thermal conductivity and heat-resistance, has been widely used to mold a thermoplastic plastic by the vacuum-forming method. The reason why the molds are required to have air permeability as stated above is that they are subjected to a vacuum suction. The reason why they are required to have thermal conductivity is that they themselves are heated in order to improve moldability, and that they themselves are cooled in order to quicken the release of the molded product from them. The reason why they are required to have heat resistance is that the their temperatures are increased in order to improve moldability and that when materials that have high molding temperatures or that are thick are molded, the heat of the material is transferred to the molds to increase their temperatures.
Generally the following are known as the methods of preparing molds and mold materials: (1) a method of making pores for breathing after a metal material is molded, (2) a method of mixing metal powders with ceramic powders by means of an evaporable binder, forming a mold from the mixture, and then sintering the mold in an oxidative atmosphere to evaporate the binder to make the entire mold porous (Japanese Patent Early-publication No. 60-46213), (3) a method of mixing metal powders with a binder, forming a mold from the mixture, and oxidatively sintering the mold to oxidatively bind the metal powders and make the entire mold porous (Japanese Patent Early-publication No. 61-67703), and (4) a method of mixing aluminum powders with an urethane-based binder as a primary binder to form a material in a wet state, injecting a hardening gas as a catalyst into the material to form a primary hardened molded body while subjecting the material to pressure molding, impregnating the molded body with a thermosetting phenolic solution as a secondary binder, drying the impregnated body, curing (secondary hardening) the dried body to obtain a porous mold material, and then processing the cured body to form an air-permeable mold (Japanese Patent Early-publication No. 5-163506), etc.
However, method (1) has such problems as wherein the traces of the processed pores are transferred to the molded workpiece, as well as wherein the method takes many processes to form a mold and to make the mold porous. Also, methods (2) and (3) have such problems as wherein since an oxidatively sintered body is obtained, the methods require much energy for sintering, and as wherein since a ceramic is formed, thermal conductivity is poor, and as wherein processing and modifying a mold is difficult. Method (4) has such a problem as wherein, although the molds obtained by it have good air permeability and thermal conductibity, the method is cumbersome since two kinds of binders are used for hardening, and as wherein since when the mold is secondary cured a phenolic resin is bled on the surface of the mold and is hardened there, the obtained mold cannot be used as it is and it is required that the surface of the mold be processed, and thus it cannot be used as a trasferring mold that transfers a fine pattern.
The present invention was made in consideration of the above problems. It aims at providing a method of producing a mold or mold material (below it will be referred as a molded body) with excellent properties. First, it has fine and contiguous pores throughout the mold and a finely-textured surface; second, it has good thermal conductivity and heat resistance; third, it can be easily prepared and at low cost, fourth, it can be used as a transferring mold and the processability is good; fifth, it has a strength sufficient for use as a mold for vacuum molding, etc.